First synthesis of ortho-trifluoromethylated aryl triflates

An efficient method for the preparation of trifluoromethylated aryl triflates (trifluoromethanesulfonates) has been developed. Treatment of 2-iodophenol with trifluoromethanesulfonic anhydride in the presence of triethylamine gives triflate 3. Then, reaction of compound 3 with FSO2CF2CO2Me and CuI in DMF–HMPA affords trifluoromethylated aryl triflate 2. This reaction sequence is also successful for meta- and para-trifluoromethylated aryl triflates. Based on this methodology, the trifluoromethylated aryl triflate 11, a key intermediate for the preparation of the conformationally restricted retinoid 8 containing a trifluoromethyl group, has been synthesized. The cross-coupling of aryl triflate 11 with vinylstannane 17 under palladium catalysis provides compound 18, the methyl ester of retinoid 8, in moderate yield.